1. Field of the Invention
The present invention relates to a thin film magnetic head including a magnetoresistance effect (MR) head section.
2. Description of the Related Art
Thin film magnetic heads including a magnetoresistance head (hereinafter referred to as "MR head") section incorporating a magnetoresistance effect device have been proposed and developed. Such a conventional thin film magnetic head includes a recording head section 40 and a reproduction head section 50. As shown in FIG. 4, the recording head section 40 features a so-called inductive-type recording head, which records information on a medium by converging a magnetic field (which is generated by allowing a current to flow through coiled wire 11) onto head cores 12 and 13 and utilizing a magnetic field leaked from a recording gap 14 (which includes a non-magnetic insulating film). The reproduction head section 50 features a reproduction head of a magnetoresistance effect type, which reads a recorded signal based on the change in the resistance of a MR device section 15 that is induced by a signal magnetic field representing the information recorded on a medium.
As shown in FIG. 4, the MR device section 15 is disposed within a shield gap 17, which in turn is interposed between an upper shield 13 composed essentially of a magnetic film (also doubling as the recording head core 13) and a lower shield 16. The MR device section 15 is insulated from the upper shield 13 and the lower shield 16 by means of insulating films 18.
Because of the requirement that the shield gap length (denoted by dsg in FIG. 4) must equal to or smaller than the shortest signal wavelength to be reproduced, the on-going demand for higher recording density has necessitate drastic reductions in the thicknesses of the insulating film 18 and the MR device section 15; for example, a head having a shield gap which is narrower than 100 nm may well be demanded in the future. However, it is very difficult to fabricate an insulating film that can provide sufficient insulation at a thickness of about 50 nm or less, and this could pose a bottleneck for the realization of high density recording. In addition, the above-mentioned structure in which the MR device section 15 is sandwiched by insulating films has problems such as the charge-up phenomenon of the MR device section 15 during a reproduction operation of the head and the loss of insulation properties of the insulating films. These problems will be aggravated as the head is pushed toward higher density recording with the use of thinner insulating films.
Accordingly, a structure including a recording head section 20 and a reproduction head section 30, as shown in FIG. 3 has been proposed. A MR device section 5 and upper and lower shields 3 and 6 are interconnected by conductive layers 10 so that the upper and lower shields 3 and 6 can also function as a lead section 19 shown in FIG. 4 (Japanese Application No. 8-34557). This structure allows for an ultra-thin film construction because the conductive layers 10 can be readily formed in thicknesses of about 20 nm or less. The aforementioned problem associated with insulating films in an ultra-narrow gap is eliminated in this structure, which does not require an ultra-thin insulating film between the shield sections and the MR device section. This structure is particularly useful in the case where artificial multilayers that exhibit GMR (giant magnetoresistance effect) properties are employed in the MR device section because a larger ratio of change in magnetoresistance (hereinafter referred to as an "MR ratio") is provided in a current direction running perpendicularly to the film surfaces than in directions within the same plane. This structure is still more useful in the case where the non-magnetic film in the GMR device is an insulating film of a tunneling type because the resistance of the overall element becomes high in the direction perpendicular to the film surfaces.
In the case of adopting such a non-magnetic film in the GMR device, it is also applicable to insert insulating films between a lead section and the shields for providing insulation therebetween, instead of interconnecting the MR device section 5 and the upper and lower shields 3 and 6 with conductive layers 10 shown in FIG. 3. The reason is that such a structure allows the insulating film 18 in FIG. 4 to retain a relatively large thickness in the entire MR device section 5, which can be implemented in the form of a relatively thin film.
FIG. 2 illustrates an exemplary MR device section 25 in a thin film head incorporating the above-mentioned tunneling-type GMR film. In FIG. 2, S represents a face of the magnetic head opposing a magnetic recording medium such as a magnetic disk. L1 and L2 represent leads for a MR device section as described above. Specifically, the leads L1 and L2 are coupled to a MR device section which includes an anti-ferromagnetic film AF, a magnetic film M1 (which is magnetically coupled to the anti-ferromagnetic film AF; referred to herein as "pinned"), and a soft magnetic film M2 capable of free magnetization rotation due to being isolated from the magnetic film M1 by means of an intervening non-magnetic insulating film T.
However, the MR device section illustrated in FIG. 2 has the following problems: Since the magnetic films M1 and M2 and the insulating film T are exposed on the head surface in the structure of FIG. 2, if they come in contact with a magnetic disk, the magnetic films M1 and M2 (which usually are metal films) temporarily enter a "flow" state and therefore allow electric communication with each other, i.e., being short-circuited. As a result, the intended magnetoresistance effect, which is based on a tunneling effect across the insulating film T, is undermined so that the element cannot provide the intended characteristics. Furthermore, since the insulating film T is usually required to be an ultra-thin film (e.g., several nanometers or less), the insulating film T becomes susceptible to insulation destruction when charged-up at both ends, possibly resulting in the destruction of the entire element.